High-speed data transmission has become very important in the business communication environment. Designers of this technology have combined modulation techniques to obtain very high-speed data transmission over simple voice-grade telephone lines. These systems have reached data transmission rates well into the tens of thousands of bits per second.
High speed data transmission also is very important in the field of paging systems where various problems are encountered. For example, as a paging receiver moves farther away from the transmitting base station, the average received power gradually degrades to a point where the bit error rate (BER) at the pager is too high for efficient communication. Various attempts have been made to develop paging products with improvements relative to complexity (size), range and cost to thereby provide the highest level of service at marketable prices.
One way to reduce the bit error rate is to simply retransmit or provide higher powered transmitters. However, there is little guarantee that the retransmission will work and high powered transmitters are very costly.
Another more advanced technique used is a retransmission scheme titled multiple forward error correction (FEC). Multiple FEC schemes code transmission more "heavily" when the signal-to-noise ratio (SNR) becomes poor. In other words, less data is sent but more error correcting bits are sent per data bit. This means that the data bits are better protected against errors. However, FEC schemes result in relatively poor performance at low SNR.
Another scheme is the multiple transmission speed scheme. This scheme reduces the data transmission rate as the SNR becomes poor to ensure that the BER remains high. However, the front end of this receiver must accommodate this change in data transmission rate and therefore becomes unnecessarily complex and expensive.
The systems described above are inconsistent in their performance and also are unnecessarily complicated and expensive.